Prediction of Covalent Interactions Between Si and B, Fe, Al or Ca in Metallurgical Grade Silicon Using ab initio Molecular Dynamic Simulations

Abstract

Boron removal from metallurgical grade silicon (MG-Si) by metallurgical process plays an important role in the production of solar grade silicon (SoG-Si). However, the effects of other impurities in MG-Si on boron removal are not yet well known. The covalent interactions between Si and B, Fe, Al or Ca in the corresponding binary and ternary structures at 1873 K are studied in present work by ab initio molecular dynamic simulations based on the Si supercell and the Si-B structure, respectively. The bond lengths of Si-B, Si-Fe, Si-Al and Si-Ca and the partial density of states (PDOS) of electric charge distribution in the binary structures indicate that the impurities Fe and Ca in MG-Si have an important effect on boron removal. The bond strength order is Si-Fe >Si-Ca >Si-B >Si-Al in the binary Si-B, Si-Fe, Si-Al and Si-Ca structures and the order of effect for impurities Fe, Al or Ca in MG-Si on boron removal is Fe >Ca >Al in the ternary Si-B-Fe, Si-B-Al and Si-B-Ca structures. The results indicate that the metallic impurities should be firstly removed prior to the boron removal for the metallurgical process.